Endotracheal intubation of a patient for anaesthesia can be achieved via direct laryngoscopy, that is the insertion of a laryngoscope blade into the throat of the patient prior to intubation. The intubation is ideally carried out whilst the patient's head is in an optimal position for open airway visual exposure, known as the “sniffing position”. To achieve the sniffing position as a patient lies on his/her back, the patient's head is elevated above a base horizontal position, the patient's neck is extended and the patient's face is maintained in the coronal plane (facing directly upwards as seen in FIG. 10) as the head moves anteriorly relative to the torso. At the correct head elevation, the oropharyngeal, laryngeal and tracheal axes of the patient's head are generally aligned. In this position, the anaesthetist or other practitioner performing the intubation has a clear view of the patient's glottis and vocal cords and intubation can take place.
It is well known that the sniffing position is highly variable and often unique to each individual patient due to anatomical subtleties. Furthermore, it is potentially non-reproducible even in one particular patient due to conditions such as pregnancy, significant weight loss or gain or trauma.
Typical anaesthetist's practice for laryngoscopy involves elevating the patient's head to an initial position, inducing the patient and then inserting a laryngoscope blade into the patient's airway. Insertion of the blade elevates the head further and tilts it back, countering the tendency for chin-on-chest rotation which accompanies head elevation. If further head elevation is required in order to place the patient into the sniffing position then it is achieved by moving the laryngoscope blade itself, which requires considerable force and risks tissue and dental damage.
Various head positioning devices have been developed to assist the anaesthetist in placing the patient into the sniffing position in order to avoid the need for subsequent movement of the laryngoscope. A known head positioning device consists of a pneumatically actuated torso/head support and expandable headrest, each having a separate air bladder that can be inflated to elevate the patient's torso/head and support it in the expandable headrest respectively. The device is disadvantageous in that it requires a costly source of compressed air and employs electromechanical valves that require cumbersome controls in order to restrict the multiple degrees of freedom of head movement that are inherent to the inflatable device. The device is also expensive and is undesirably distracting for the anaesthetist who needs to simultaneously perform the laryngoscopy and direct the pneumatic controls.
Another known head positioning device includes a head support and articulated arms that elevate the head support above a base position, the articulated arms and the head support device having a number of lockable articulated and sliding joints that can be locked once the sniffing position is achieved. The device may be actuated and locked using electronic or mechanical controls for each lock and using mechanical or non-mechanical drivers for each articulating or sliding element of the joints. This device is disadvantageous in several respects. Firstly, the patient's head has multiple degrees of freedom of movement, such that it is difficult for the anaesthetist to accurately identify the sniffing position. Secondly, the amount of manoeuvring of the device that is required to achieve the sniffing position over complicates the procedure. Thirdly, the complex construction of the device and of the control units necessary to operate the device increase manufacturing costs and complexity and increase the risk of malfunction and consequential patient safety issues.